The distribution of methylamine in the Jovian atmosphere
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An estimate of the methylamine concentration on Jupiter has been made. The maximum production rate of 6 × 10 4 cm −3 (Jovian day) −1 occurs in the vicinity of 60 km above the ammonia cloud layer. If the downward transport of methylamine equals the production rate, then the volumetric mixing ratio is 3 × 10 −11 .Keywords:
Atmosphere of Jupiter
Mixing ratio
Jupiter (rocket family)
Production rate
Galilean moons
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The spectrum of Jupiter has been recorded on April 12, 1996, between 2.75 and 14.5 mu m, with the grating mode of the Short-Wavelength Spectrometer of ISO (Infrared Space Observatory). The resolving power is 1500 and the sensitivity limit is better than 1 Jy. The corresponding S/N ratio is better than 1000 at 2.75 mu m, 4000 at 5 mu m and 20000 at 12 mu m. The main preliminary results of the grating observations are (1) at 3 mu m, the first spectroscopic signature, probably associated with NH_3 ice, of the Jovian cloud at 0.5 bar and (2) the first detection of a thermal emission at the center of the CH_4 nu_3 band at 3.3 mu m, showing evidence for a high temperature in the upper jovian stratosphere (about T=800 K at P=0.16 mu bar). A modelling of the whole spectral range will be presented, with implications on the jovian thermal profile and on the mixing ratios and/or vertical distributions of the atmospheric constituents. A preliminary analysis of these data can be found in Encrenaz et al (submitted to Astron. Astrophys., 1996).
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An estimate of the methylamine concentration on Jupiter has been made. The maximum production rate of 6 × 10 4 cm −3 (Jovian day) −1 occurs in the vicinity of 60 km above the ammonia cloud layer. If the downward transport of methylamine equals the production rate, then the volumetric mixing ratio is 3 × 10 −11 .
Atmosphere of Jupiter
Mixing ratio
Jupiter (rocket family)
Production rate
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Atmosphere of Jupiter
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The Galileo probe mass spectrometer determined the composition of the Jovian atmosphere for species with masses between 2 and 150 amu from 0.5 to 21.1 bars. This paper presents the results of analysis of some of the constituents detected: H2, He, Ne, Ar, Kr, Xe, CH4, NH3, H2O, H2S, C2 and C3 nonmethane hydrocarbons, and possibly PH3 and Cl. 4He/H2 in the Jovian atmosphere was measured to be 0.157 +/- 0.030. 13C/C12 was found to be 0.0108 +/- 0.0005, and D/H and 3He/4He were measured. Ne was depleted, < or = 0.13 times solar, Ar < or = 1.7 solar, Kr < or = 5 solar, and Xe < or = 5 solar. CH4 has a constant mixing ratio of (2.1 +/- 0.4) x 10(-3) (12C, 2.9 solar), where the mixing ratio is relative to H2. Upper limits to the H2O mixing ratio rose from 8 x 10(-7) at pressures <3.8 bars to (5.6 +/- 2.5) x 10(-5) (16O, 0.033 +/- 0.015 solar) at 11.7 bars and, provisionally, about an order of magnitude larger at 18.7 bars. The mixing ratio of H2S was <10(-6) at pressures less than 3.8 bars but rose from about 0.7 x 10(-5) at 8.7 bars to about 7.7 x 10(-5) (32S, 2.5 solar) above 15 bars. Only very large upper limits to the NH3 mixing ratio have been set at present. If PH3 and Cl were present, their mixing ratios also increased with pressure. Species were detected at mass peaks appropriate for C2 and C3 hydrocarbons. It is not yet clear which of these were atmospheric constituents and which were instrumentally generated. These measurements imply (1) fractionation of 4He, (2) a local, altitude-dependent depletion of condensables, probably because the probe entered the descending arm of a circulation cell, (3) that icy planetesimals made significant contributions to the volatile inventory, and (4) a moderate decrease in D/H but no detectable change in (D + 3He)/H in this part of the galaxy during the past 4.6 Gyr.
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High signal-to-noise spectra of the Jovian aurora at UV wavelengths obtained using the International Ultraviolet Explorer Observatory (including the brightest Jovian aurora observed to date) set strigent upper limits for sulfur and oxygen emissions, which would be associated with the precipitation of energetic heavy ions in the upper Jovian atmosphere if they were solely responsible for Jovian auroral processes. Model calculations of heavy ion precipitation and corresponding estimates of the associated sulfur and oxygen UV emissions previously carried out suggest emission values for 1304 A OI emission that are at least 30 times larger than the upper limit values set by the IUE observations reported. On the other hand the observed (feature of SII at 1256 A of 2 kR) is quite comparable to the theoretically predicted emission intensity. Taken together these observations and calculations suggest that electron as well as ion precipitation play a role in Jovian auroral processes. In light of earlier X-ray observations and in-situ plasma observations that suggest energetic heavy ion precipitation in the Jovian auroral zone, a scenario is suggested where heavy ion auroral energy deposition is concentrated at altitudes below the homopause. Electrons with energies of 10 to 30 keV are responsible for the bulk of the observable UV and EUV emissions since they deposit their energy above the methane absorbing layer defined by the homopause.
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